The present invention is directed to a rock drill with an axially elongated shank with a chucking shank part at one end, a drilling shank part extending from the chucking shank part with at least four conveying flutes in the drilling shank arranged in parallel relation and a drilling head formed of hard metal secured to the other end of the shank with four removal flutes spaced around the circumference of the drilling head. The transverse cross-sections of the conveying flutes and the removal flutes are in register.
Rock drills of the above type are used to cut bore holes in rock, concrete, masonry and the like. It is known that such rock drills wear out very rapidly in the region of the drilling head when drilling in a hard strata. Therefore, rock drills are formed of a hard metal and the term "hard metal" is meant to describe sintered or fused carbide, silicate, boride or their alloys.
Such a rock drill is disclosed in U.S. Pat. No. 2,673,716. This rock drill has a drilling head formed entirely of hard metal connected to a drilling shank with the drilling head having four drilled material removal flutes extending in the axial direction of the drilling head with the flutes uniformly spaced around the circumference of the head. The drilling head has a centrally disposed projection for connecting the head to the drilling shank, whereby the projection extends into a corresponding recess in the drilling shank.
The continuous removal of the drillings or drilled material by this known rock drill during operation occurs through the removal flutes running in the axial direction of the drilling head to drillings conveying flutes in the drilling shank. The flutes in the drilling shank extend in a helical manner and register with the removal flutes on the drilling head. Since the transverse cross-section of the removal flutes in the drilling head are of equal size, the same amount of drillings is carried away through each removal flute during the drilling operation. When removing very soft or brittle material, jamming of large grain drillings in the removal flutes can occur. Additional drillings collecting in the removal flutes press radially outwardly against the borehole wall so that on one hand an increased torque must be applied to drive the rock drill while on the other hand damage to the borehole wall takes place, particularly due to off-center running of the rock drill.